Circuit-breaking switch



June 15, 1948. c, E BERRY 2,443,338

CIRCUIT-BREAKING SWITCH Filed June 22, 1943 .Zzzv e12, Z01

Patented June 15, 1.948

CIRCUIT-BREAKING SWITCH Cyril Ernest Berry, Johannesburg, Transvaal, Union of South Africa, asslgnor to Southern Engineering Supplies (Pty.) Ltd., Johannesburg, Transvaal, Union of South Africa Application June 22, 1943, Serial No. 491,834 In the Union of South Africa February 3, 1943 1 Claim.

This invention relates to circuit-breaking switches; and particularly to such switches operated by overload coils, where extreme speed of operation is not of first importance.

An object of the invention is to provide an overload switch that can be completely manufactured in the form of a single unit ready for operation upon being mounted in the field of the actuating magnet and connected in the electrical circuit it controls.

A further object is to provide an overload switch comprising a dashpot and the dashpot liquid ready provided by the manufacturer and sealed against loss or deterioration.

Another object is to arrange for the circuit breaking to take place in oil. A further object is to provide very simple means for adjusting the switch to operate at different degrees of overload.

The invention comprises a switch unit consisting of a totally enclosed casing, comprising external terminals and means within the casing movable to complete and break electrical connection between said terminals, said means being movable by an external magnet to break said connection.

In the preferred form of the invention, the movable means comprises two parts, one of which is a contactor arranged to complete and break electrical connection between spaced contacts which are fixed and exposed within the casing and are connected respectively to the external terminals; the second part being susceptible to a magnetic field, and having a lost-motion connection with the contactor. Also, the movable means comprises adashpot element, such as a dashpot piston; and the casing provides the complemental dashpot element, such as the cylinder with which said piston co-operates. The casing contains a suitable liquid, such as oil, which acts as dashpot liquid. The unit has a working position in which the liquid and the piston tend gravitationally to be operatively assembled with the dashpot cylinder, and in which the casing positions the movable means ready for upward displacement from such gravitational position; and when the unit is in such working position, the fixed contacts are submerged in the oil; the oil volume in the casing being sufficiently great for this purpose.

As a rule, the unit also comprises means so to secure it to a magnetic coil structure that the unit may be adjusted in the direction of the axis of the coil. The securing means may comprise a bracket spaced laterally from the casing and slotted suitably to receive a clamping screw,

the slotting extending vertically when the unit is in its working position; and the lug may be provided with a pointer directed horizontally when the unit is in its working position..

The invention also comprises the combination, in an overload switch of a solenoid coil structure, a, solenoid core, and a casing in which said core is totally enclosed, the casing being movably attached to the coil structure in a position in which the coil and core are co-axial. Preferably, an external suriace'oi' the coil structure is provided with a vertical scale; and the casing is provided with a pointer co-operating with said scale to indicate the degree of penetration of the easing into the coil bore.

An example of the invention is shown accompanying drawings in which Figure 1 is a vertical section of a switch unit according to the invention.

Figure 2 shows the unit operatively assembled with its actuating coil.

The switch unit 2 comprises a hollow casing 3, 4 consisting of the body element 3 and the cover element 4. These parts are electrically non-conducting and impervious to liquid; and may be made of Bakelite. The body element is shaped to provide the cylindrical or other chamber 5 suitable to enclose and allow the vertical movement of the moving parts hereafter described; and also to provide the dashpot cylinder 6 beneath chamber 5. The dashpot cylinder is generally of smaller diameter than the chamber 5; in which case it is desirable that the casing portion 1 between them should be tapered downwardly to avoid a shoulder that might hinder the descent of the dashpot piston into the cylinder.

Sealed in the wall of chamber 5 are two metallic elements that provide internally the pair of contacts 8, 8, and externally the terminals 9, 9 for interpolation in the circuit to be controlled.

The cover element 4 screws onto the body element 3 and thereby closes the casing as a whole. Beside the portion 4 which functions merely as a cover, the cover element includes the hollow vertical extension 4 which encloses and forms a guide for the core element of the moving part of the switch.

The movable part of the switch comprises a body element I8 that is conveniently made of Bakelite. To its upper end is secured a piece of light sheet iron bent to cylindrical shape and constituting the iron core ii for co-operation with the actuating solenoid coil. As is common practice, the cylindriform plate is not continuous circumferentially; its edges I2, l2 being spaced apart to avoid hysteresis currents.

The lower end of the body I8 is shaped to form the dashpot piston l 3 which fits within the dashpot cylinder 6 with appropriate peripheral clearance to ensure the desired slow rise of the body. The stem portion l4 of the body immediately above the piston I3 is of small diameter to avoid excessive displacement of the dashpot liquid l5.

The bridging contactor I8 is a washer-shaped piece of metal through the central hole ll of which the body In is free to move; and it normally rests on the internal contacts 8, 8 to complete the controlled circuit represented by the leads l8, l8 soldered to the terminals 9,9. The annular width of the contactor is such as to make extensive contact with the contacts 8, 8. A spring l9 normally holds the bridging contactor l8 down on the fixed contacts 8, 8. The piston i3 is made of greater diameter than the hole I! of the contactor, in order to pick up the contactor when the body unit rises.

In manufacturing the switch unit, the movable members II), II and I6 are positioned within the casing and so much oil is is poured into the body portion 3 of the casing as is necessary to ensure that the fixed contacts 8, 8 are well submerged in the oil when the unit is standing with its axis 20 vertical. The cover 4 is then screwed on; the joint between the body and the cover elements being hermetically sealed as by means of shellac. The manufacture of the unit isthereby completed and it becomes an article of sale; although it is preferred at this stage to provide means indicated by 2| for fixing the unit to the actuating coil structure.

Figure 2 shows the unit operatively assembled with the overload coil that causes its actuation and with the circuit that it controls. In that figure, 22 indicates the panel on which is fixed the frame and bobbin structure 23 of the actuating coil 24. The leads for said coil 24 are indicated by 25, 25. The extension 4* of the cover element 4 is inserted from below into the bore 3! of the solenoid coil 24 by which it is to be actuated so bringing the core ll within the field of said coil 24. It is convenient to make said bore 3| of the coil and the extension A of such diameters that the latter is a sliding fit in the former. The degree of penetration of the latter into the former is then adjustably fixed by the means 2|. The extent of such penetration determines the magnitude of the overload current at which the switch will operate.

The fixing means 2| for securing the unit to the coil structure 23, 24 whilst allowing the unit to be adjusted vertically with respect to the coil, comprises a clip 26 provided with a bracket 21 that is vertical when the unit is in its vertical working position and which is so spaced laterally from the unit as to be at or near an external surface 28 of the coil structure 23. Said bracket 21 is elongated vertically and is formed with a vertical slot 29 through which the shank of the screw 30 can pass and screw into said structure 23. The screwing home of the screw 38 thus secures the unit 2 in position with reference to the coil 24 and the slot 29 enables said position to be adjusted in the axial direction as mentioned above. The corresponding values 01' the overload current are represented on a. vertical scale 32 marked on the surface 28; and the lug 21 is provided with a horizontal pointer 33 that indicates the current value corresponding to the vertical adjustment of the unit.

When the unit is thus fixed in position, the oil l5 occupies the dashpot cylinder 8 and covers the contacts 8, 8. If no overload is present the movable unit rests at its lowest position in the casing, with the piston l3 at the bottom of the dashpot, the core H well below the upper end of the extension 4", and the contactor l6 resting on the contacts 8, 8 and completing the circuit between them.

Upon the occurrence of an overload of the magnitude corresponding to the height at which the unit has been fixed in relation to the coil 24, the movable unit is projected upward, causing the piston l3 to strike and lift the contactor I 6 and thereby break the controlled circuit I8, I 8. Eventually said circuit is restored by the fall of the movable elements upon the overload being removed.

The dashpot slows down this rising movement sumciently to ensure that the circuit is not broken by a momentary surge of current. The lost motion between the piston l3 and the contactor It has the same efiect and moreover ensures that when the contactor is lifted away from the contacts 8. 8 that is done quickly. The fact of the oil level being above the fixed contacts 8, 8 protects said contacts and the contactor against deterioration by the circuit being broken and remade at said contacts. In order further to ensure their long eifective life they are in practice made of silver. The total enclosure of the oil ensures that it cannot be lost during the handling of the unit and preserves it against deterioration by oxidation or by dust becoming mixed with it.

I claim:

A circuit breaker switch unit comprising a hollow casing consisting of at least two parts hermetically jointed together, said casing providing at its lower end the cylinder of a dashpot, and at its upper end an enclosed constraining guide; a movable switch member enclosed within said casing and comprising at its lower end a piston for the dashpot, and at its upper end a solenoid core enclosed and constrained by said guide; stationary contacts supported by said casing, and means to connect said contacts to electrical leads outside said casing; a contactor member arranged to bridge said contacts, and a spring acting to assist gravity to urge said contactor member to rest on and bridge said contacts, the said bridge member and spring being contained within said casing; said bridge member being apertured for the passage of said solenoid core but not said piston through it; said piston having a lost motion connection with said bridge member to lift it; an insulating liquid within the casing to provide the dashpot liquid and to cover said contacts when the-unit is in a vertical position with said contacts materially horizontal; means to secure the unit to a solenoid coil in such a way that the unit may be adjusted relatively to said coil in the direction of the coil axis; said securing means comprising a bracket spaced lat- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 441,542 Enholm Nov. 25, 1890 796,646 Hewlett Aug. 8, 1905 835,493 Baldwin Nov. 13, 1906 Number Number 1 293,862

Name Date Downes et al. July 16, 1918 Johnson -1 Dec. 17, 1918 Uchida, July 22, 1919 Kane June 6, 1922 Denlson July 1, 1930 Prince Dec. 26, 1933 Larson Dec. 15, 1936 Wilhelm May 16, 1939 Jarreau et a1 Sept. 19, 1939 Cofley Sept. 26, 1939 FOREIGN PATENTS Country Date Great Britain Oct. 2, 1929 

